Dominant X linked retinitis pigmentosa is frequently accounted for by truncating mutations in exon ORF15 of the RPGR gene.

Retinitis pigmentosa (RP) is a group of progressive hereditary disorders of the retina in which various modes of inheritance have been described. The X linked forms of retinitis pigmentosa (XLRP, MIM 268000) are among the most severe owing to their early onset, leading to significant vision loss before the fourth decade. Five XLRP loci have been localised by linkage: RP2 (MIM 312600), RP3 (MIM 312610), RP6 (MIM 312612), RP23, and RP24 (MIM 300155). The major loci, RP2 and RP3, map to Xp11.4 and Xp21.1, respectively. RP3 is accounted for by mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. RP3 accounts for 70% of XLRP, 4 but until recently only 20% of mutations were identified in RP3 families, suggesting genetic heterogeneity at this locus. This hypothesis has been excluded by the discovery of a mutational hot spot in a new RPGR exon, ORF15. In 1997, we reported on X linked RP in nine families with constant and severe expression in carrier females. In this series, onset was delayed and sometimes milder in females than in hemizygous males. However, in all the pedigrees in the present report, some females were as severely affected as